Setting source IP when adding a static route / set src

[SwimGeek]

Hi

I see you can use 'set src' in a route-map, to set the source IP when a route is installed.

I was hoping to set a source IP for a static route. Is there a reason this is not supported?

https://docs.frrouting.org/en/stable-10.2/static.html

[ton31337]

Which use case do you have in mind? set src is mostly used with ip[v6] protocol ... route-map ... to set the source IP to the arbitrary destination. One use case example would be BGP unnumbered.

[SwimGeek]

Hi

It sometimes happens that a router connected to peering points will use the peering point IP as source address when doing things like apt-get for package updates or running offsite backups.

Wanted to add a static route which sets the source IP in frr.conf - just to keep all the static routes in one place.

[ton31337]

Can you show how are you trying to use it?

[SwimGeek]

Very similar to adding a route in Linux:

ip route add n.n.n.n/32 via m.m.m.m src x.x.x.x

...when routing to n.n.n.n/32, set source IP to x.x.x.x

[ton31337]

I meant how do you do in frr.conf?

[SwimGeek]

as far as I can see this can't be done in frr.conf - not supported in the syntax for adding a static route

[ton31337]

It works for me fine.

route-map a permit 10
 set src 192.168.10.139
exit
!
ip route 100.100.100.201/32 192.168.10.1
!
ip protocol static route-map a
!

Output:

donatas# show ip route 100.100.100.201/32
Routing entry for 100.100.100.201/32
  Known via "static", distance 1, metric 0, best
  Last update 00:00:57 ago
  * 192.168.10.1, via wlp0s20f3, rmapsrc 192.168.10.139, weight 1

In the kernel:

# ip route show 100.100.100.201
100.100.100.201 nhid 16 via 192.168.10.1 dev wlp0s20f3 proto 196 src 192.168.10.139 metric 20 

[ne-vlezay80]

Why set nexthop attribute from ip protocol?

[SwimGeek]

I was trying to set the source IP, without needing a route-map - but I figured out another solution.

The route map + 'set src' way of doing it can also work for what I need.